The present invention relates to draft gears and, in particular, to an improved friction draft gear having superior means of dissipating and absorbing draft forces.
In prior art draft gears, as exemplified by U.S. Pat. No. 3,227,288, which is assigned to the assignee of the present invention, draft forces impinging upon a wedge extending from the draft gear are dissipated in the housing of the draft gear through a series of friction shoes. The end of the draft gear housing in which the wedge and shoes are located has an inwardly tapered friction surface such that as the wedge is forced into the interior of the housing, frictional force increases between the shoes and the housing. The shoes in turn abut a generally circular follower member or plate which is forced against the shoes by resilient means such as a stack of cushioning pads. As shown in U.S. Pat. Nos. 2,139,701 and 2,159,457, a series of concentric springs can be used in place of the cushioning pads.
While the draft gear of U.S. Pat. No. 3,227,228 has a high shockabsorbing capacity, a problem has occurred at the interface of the shoes with the follower plate. Since the shoes travel both axially and radially inwardly during absorption of draft forces, over time the shoes tend to gall the metal and carve paths into the abutting face of the follower plate. This creates an accumulation of metal at the edges of the shoe contact pattern, preventing greater travel of the shoes along the follower plate. If larger draft forces than normal are experienced by the draft gear, often the accumulated material prevents required travel of the shoe, creating substantial stresses which result in erratic operation and, at times, cause the shoes to break within the draft gear. The draft gear then must be either replaced or rebuilt. The prior design for the shoes, wedge and follower also created some difficulties in maintaining the components of the draft gear in position during assembly.